better understand and predict the process of turning genes on, which involves
copying genetic instructions from DNA
into RNA. His work describes how and
when proteins congregate to instigate
this process, which keeps cells functioning properly throughout life.

Cissé was encouraged by physicist
Carl Wieman, who won the Nobel Prize
in physics in 2001 for his work on Bose-Einstein condensates, to apply for a
fellowship to work at a big research university. As a result, Cissé spent a summer
at Princeton University learning soft
condensed matter physics, the study of
properties of liquids and other materials that can change shape, as it applied to
randomly packing M&M’s into a jar. That
work resulted in his first scientific paper,
published in 2004 in Science.

During postdoctoral research, Cissé
made what seems like a simple tweak to a
single-cell microscopy technique, called
PALM, that made his future discoveries
possible, says Taekjip Ha, a biophysicist
at Johns Hopkins University who was
Cissé’s graduate mentor at the University
of Illinois at Urbana-Champaign.

With PALM, Cissé examined RNA
polymerase II in action. The enzyme
is crucial for turning DNA instructions
into the RNA messages that are read to
build proteins.

“He didn’t just use PALM to obtainpretty images,” Ha says. Cissé added “atime dimension.” Rather than takingstationary snapshots, Cissé made mov-ies that showed that RNA polymerase IIforms clusters that fall apart once theirjob is done. The discovery was publishedin 2013 in Science.

“That finding was pretty provocative,”
Ha says. Until then, researchers had
thought that RNA polymerases formed
stable factories that would park near a
gene’s starting point and idle, waiting
for other proteins to give them a push to
turn the gene on.

A few years later, in 2016, Cissé and
colleagues reported in eLife that the
amount of time an RNA polymerase cluster stays together determines how many
RNA messages are produced from a gene,
a measure of how active the gene is.

In his latest studies, published in
the July 27 Science (SN: 7/21/18, p. 14),
Cissé and colleagues present evidence
that proteins involved in turning on
genes rapidly coalesce into concentrated droplets just before the process
of copying DNA into RNA begins. Like
water molecules condensing into a raindrop and then evaporating, proteins can
quickly form these droplets and then
disperse.

Individual proteins spend only seconds in the condensates, but collectively
the molecules turn on genes. And bubbles of condensed proteins may interact
with other bubbles, sometimes several,
to turn on multiple genes at once.

The idea is controversial. Some
researchers argue that this condensation process isn’t necessary to start gene
activity.

To Cissé, knowing about these “
bubbles” means researchers can draw on
the physics of condensation — such as
knowledge about cloud formation, rain
and snow — to understand how gene-activating proteins behave and predict
what will happen next. s

At 17, Cissé moved to North Carolina
to learn English. Later, on registration
day at North Carolina Central University
in Durham, a historically black college,
a physics professor quizzed him about
math and science and suggested Cissé
major in physics. Then came the magic
words: “We have a grant from NASA.”
Recalling his cosmic childhood dreams,
Cissé became a physics major.

Now 35, Cissé is “everything you couldwant in a young scientist,” says AnthonyHyman, a biologist at the Max PlanckInstitute of Molecular Cell Biology andGenetics in Dresden, Germany, whofollows Cissé’s work. “He’s dynamic,enthusiastic and interested.”These days, Cissé, a newly mintedAmerican citizen, is breaking para-digms instead of electronics. He andcolleagues are making movies withsuper-resolution microscopes to learnhow genes are turned on. Researchershave spent decades studying this fun-damental question.